THE IMPORTANCE AND USE OF THE DETERMINED CARRYING CAPACITY OF RANGELANDS


C. Wayne Cook
Dept. of Rangeland Ecosystem Science
Colorado State University

The carrying capacity of a range is the number of animals that can be grazed without undue harm to the soils and vegetation. It is always assumed that when soils and plants are unharmed, animals on the range are likewise unharmed, but this is not always correct. Nutrition may be limiting for animal welfare on otherwise properly grazed ranges.


Some rangeland managers say that there can be no grazing capacity assigned to any particular parcel of land such as a fenced pasture or a range site. Production does indeed vary from year to year on any area of rangeland. As a result, the carrying capacity must be flexible, generally not using more than 50% of the total forage available from one year to the next. Over time there can be more use from year to year. For cattle, it is suggested that the breeding herd be at 65 to 70% of average capacity among years. Thus, during good years steers can be added; and during dry years less than the full breeding herd with no replacements and no cull animals. No steers are carried over during dry years. They are sold as weaner calves or no older than yearlings.


Estimated carrying capacities for tracts of rangeland must be recognized as necessary and useful for management. Rangelands are sold on the basis of animal units/acre capacity or animal units capacity/ranch such as a 1500-cow ranch. IRS and estate transfer tax is based upon AU capacity. Damages wrought on rangelands by pipelines, surface mining, road construction, etc. are evaluated on the basis of animal unit months of capacity lost to normal operations of the ranch. Eminent domain purchases and misrepresentation of sales are settled in lawsuits based on carrying capacity of the land involved. Calculated carrying capacity of range sites is a means of comparing the value of rangelands of different types; for example, meadows, rolling plains, breaks, brush types, etc.


Grazing capacity may depend upon frequency of drought years, species of animals used, size of animals (breeds), physiological function of animals, season of use or grazing system used, and distribution of animals.

Examples of the above noted complications are:

• Sheep are more adaptable to rough terrain and browse range than cattle;
however, common use by both with appropriate numbers of each would
have higher capacity than either class alone.


• Animal breeds averaging 1200 lbs/cow consume about 31% more forage
than breeds weighing only 915 lbs/cow.


• Animals in lactation or growing consume about 19% more than animals in
gestation or maintenance.


• Seasonal grazing, such as on the northern desert shrub types, if grazed
during the spring, has only half the carrying capacity as when grazed in
the winter because only one growing period (April 1 to June 15) is available for
recovery after grazing.

 


• Management plans or grazing systems that provide flexibility in grazing
intensity with relation to fluctuating forage production from year to year is
less wasteful of the range forage than established numbers that leave
unused herbage during good years, and slightly overgrazed during drought
years (this practice requires conservative stocking and less overall capacity
than flexible management systems).


• Hazards, such as down timber and thick brush may reduce grazing capacity by
as much as 60%.

 


• Distribution of animals by placement of water and salt, along with
some trail construction, can increase capacity as much as 30 to 50%.


In case a ranch or an allotment on government land is divided into pastures by fences the management becomes a matter of the suitability of each pasture. It is important that each pasture is rather uniform or similar throughout. Any variation in vegetation cover should be slight or if different vegetation types are present the areas of such should be small and generally few because management practices are assumed to affect all of the pasture in the same way.


The capacity for any single species of animal on a specific area of range depends upon the total aggregate of plant species and of all other animal species using the area. Thus, common use of mountain range by sheep and cattle in numbers representative of suitability will have 20 to 25% greater capacity than single use by either species. The reasons for this are the differences in degree of use of plant species by different animal species.


The practical application of carrying capacities are many and varied. As mentioned before, when rangelands or ranches are bought, sold, or traded, the value is calculated by means of a carrying capacity figure for them and the going grazing price/animal unit on a year-long basis. Thus, all rangeland brokers must somehow establish a carrying capacity. Allotments on federal lands are based upon the calculated carrying capacity of the land. Grazing permits on all Indian lands are based upon calculated carrying capacities of the land. Charges for grazing in both of the above cases are based on an animal unit month of grazing stated in the permit.


Rangeland brokers generally arrive at capacity of a ranch by comparison of neighboring ranches previously sold in the area. Grazing capacity for a particular ranch may be arrived at primarily by talking to the manager about how many cows, bulls, replacements, steers, and horses are run on the ranch. For instance, a manager may answer that he tries to keep about 600 cows, 15 bulls, 50-60 replacements, and 10 horses. Thus, about 675 Au's are run on the ranch, but this number is not constant from year to year by any means. This commitment by the manager generally disregards the drought years when it was necessary to cut back animal numbers rather substantially. It also does not include range supplements or the amount of harvested forage fed during bad weather. Thus, the carrying capacity used by a real estate brokerage will be higher than the actual capability of the range forage, and as a result, should be considered a more general figure for equating the value of rangeland in a particular area rather than the actual carrying capacity of the range involved.


How then does a scientific approach for calculating grazing capacity of a ranch or a parcel of rangeland occur? The procedure is generally recognized as an "ocular reconnaissance range survey". First, it consists of obtaining production of vegetation by species composition, and multiplying this by the degree of utilization expected; thereby obtaining the actual pounds/acre of useable herbage or "forage" (Table 1). Second, we need the expected daily consumption of the animals that will be grazing the range in question. Table 2 describes some calculations of air dry matter consumed per day under normal range conditions without supplements.

TABLE 1- CALCULATING CARRYING CAPACITY FOR CATTLE

ON A YEARLONG BASIS
SPECIES
PRODUCTION
UTILIZATION

AVAILABLE
FORAGE
 
(#/ACRE)
(%)
(#/ACRE)
Western Wheatgrass
600
55
330.0
Galleta grass
200
30
60.0
Big Sagebrush
250
15
37.5
Winterfat
100
35
35.0
Bigalow Sagebrush
100
35
35.0
TOTAL
1250
39.8(avg)
497.5

 

 

TABLE 2 - AVERAGE WEIGHT, DAILY GAIN, CONSUMPTION OF AIR-DRY MATTER AND ANIMAL UNIT EQUIVALENT FOR VARIOUS KINDS OF LIVESTOCK DURING VARIOUS SEASONS
KIND OF ANIMAL
SEASON

AVERAGE WEIGHT

(lbs)

GAIN PER DAY

(lbs)
DAILY CONSUMPTION (lbs/day)
ANIMAL UNIT EQUIVALENT
INTAKE PER ANIMAL (lbs)
Ewe & Lamb
Spring
134
0.5
6.1
0.19
4.55
Summer
142
0.5
7.3
0.23
5.14
 
Average
139
0.5
6.9
0.22
4.96
 
Winter
139
---
5.1
0.16
3.67
 
Average
139
---
5.8
0.18
4.17
Cow & Calf
Spring
892
2.14
32.1
1.02
3.60
 
Summer
956
1.42
35.3
1.12
3.69
 
Average
919
1.84
33.4
1.06
3.63
 
Winter
910
---
29.8
0.94
3.27
 
Average
914
---
31.6
1.00
3.46
Steer
Spring
590
2.25
20.4
0.65
3.46
 
Summer
775
1.75
24.9
0.79
3.21
 
Average
667
2.04
22.3
0.71
3.34
 
Winter
435
0.39
15.4
0.49
3.54
 
Average
551
1.22
18.8
0.59
3.41
Dry Cow
Spring
955
----
24.0
0.76
2.51
 
Summer
1116
----
29.4
0.93
2.63
 
Average
1022
----
26.2
0.83
2.56
 
Winter
1037
----
26.2
0.83
2.53
 
Average
1029
----
26.2
0.83
2.55
Gain per day is based upon lamb, calf, and steer body weight change only.
Intake per animal includes forage eaten by lamb or calf prorated on average weight of ewe or cow, and on a 100% lamb and calf crop.

 


Following are some calculations of air-dry range forage consumed by various species of animal and by various classes of animal within species.

• Dry cow that weighs 1000# will consume 32.7 #/day

• Wet cow and calf that weighs 1000# will consume 36.4#/day

• Year-long range cow that weighs 1000# (6 months dry and 6 months wet) will consume 34.5#/day or 1035#/month

• During spring-summer steer or heifer weighing 667 pounds will consume 22.3#/day or 669#/month

• Dry ewe weighing 140# will consume 5.1#/day

• Wet ewe weighing 140# with a lamb will consume 6.9#/day

• A ewe year-long grazing (6 months dry and 6 months wet) will consume about 6.0#/day


The final calculation (Table 1) uses the pounds/acre of forage consumed which was 497.5 pounds (total vegetation growth was 1250 pounds per acre). Thus, this pasture had a carrying capacity of 1.91 acres/animal unit month year-long (948# required per cow month divided by 497.5# per acre of useable herbage).

• Tables 1 and 2 display the consumption of various animal units.

• Dry cow weighing 910 pounds is 29.8#/day x 30 = 894#/month animal unit

• Wet cow weighing 919 pounds is 33.4#/day x 30 = 1002#/month per animal unit

• Year-long grazing by a cow weighing 914 is 31.6#/day x 30 = 948#/month for 6 months dry and 6 months wet


It is possible to arrive at a satisfiable grazing capacity by simply observing the degree of use made of the dominate palatable plants. If the dominate palatable plants are not used over 50% to 55% on the average range areas and not used over 65% on the smaller lower meadow like areas then the utilization is appropriate. If a person knows the plant species and takes pains in his estimates and makes the estimates near and perhaps again at the end of the grazing season.


It's expressed by many range managers that a reasonable approach to carrying capacity is by means of placing what is believed to be a reasonable number of animals of any species or a combination of any two species on the area. The last choice, of course, complicates the system. Therefore a number of only a single species of animals is recommended unless the estimator has a large amount of experience.


• At various intervals during the grazing season, the actual use on at least the major species of plants is estimated as light, medium or heavy use. At the second interval during the season such as 75% through the season a similar estimate of utilization is estimated for all of the major plant species.


• If at this time, when 3/4 of the season has passed, it is hoped that only an average of 40% to 50% utilization is made on the major forage species. As a check, it is preferable if there is not more than 60% use on the major species by the end of the grazing season. Some range managers use 75% as optimum use by the end of the season but this is too intense to maintain the normal vigor for existence of the major or more palatable species in the plant expression that is sought.


• It could be that you have a single species that is so highly palatable and also rather sparse that you may choose to sacrifice the species in order to fully use the major plant species for production of export meat from the ecosystem that will optimize the expenditure of cultural energy per unit of land production.


The classification of plant species as indicators of condition of the range is indeed a major problem for modern range management. It is however well known that the more palatable plants are replaced with less palatable plants when ranges are overgrazed. However, a particular plant species may be relatively unpalatable during a particular season or on a particular site but may be readily eaten during another season or on another site where plant association is different. Seldom is the presence or absence of a single plant species used as the only indicator of range condition or range use.

• A range in a deteriorated condition displays a greater abundance of the less palatable plants; whereas, a range in good condition has a greater abundance of plants that are known to be more palatable under most conditions.
• The identification of plants as indicators generally is a product of opinion based upon general observation. However, a quantitative confirmation of such classifications of indicator species for broad range types is desirable if the decision is obvious.
• A highly palatable plant species is sometimes called a sacrifice plant because it is readily consumed by many animal species under various conditions. Therefore it will disappear even with light utilization of the entire flora present.


• In a study of the cold desert shrub areas of Utah and Nevada it was concluded that most desert plants can be grazed in late spring only if herbage removal is at the level of 30 percent or below. Utilization of 50 percent or more during this season is extremely detrimental. It was also found that forage removal during the winter and again in the spring could not exceed 30% during any one season if satisfactory range condition is to be maintained.

Livestock numbers with respect to breeds and size are of primary importance:
• The European breeds of cattle that are being used in the western United States as range animals vary in female cow weights and weaning weights of calves. The Hereford cows may average 850# per female cow whereas some European breeds may have cows that weigh as much as 1300# with calves averaging 150# more weight at weaning than the common Hereford calf of the same age.
• This appears to give the European breed a decided advantage but this is not really true. If the range forage consumption per breed is considered, the heavier weight is really no advantage for the European breeds. The grazing capacity should be calculated on the total weight of female cow and her calf that grazes beside her. The forage consumption is approximately the same for the average per pound weight for each breed cow and calf, which makes the production cost per pound of calf produced the same for each breed.
• Many western ranchers have felt that the European breeds, because they produced a bigger calf at weaning made the larger European cattle more profitable. This is not true. After a year or two you will soon find that you cannot run the same number of female European cattle as with your initial Hereford herd of earlier years, because you will have a deteriorated range from too many big cows with big hungry calves.

• Generally it is recognized that spring use should not be more than 30% to 40% of the foliage cover and when a range is used for only fall or winter use not more than 55% of the total foliage cover for the grazing year should have been removed. These figures are taken from what we call average overall seasonal use of rangelands which are generally known to be dry with about 8 to 12 inches of moisture annually.
• Using these utilization figures, which have been taken from several research studies from different range areas of the western states, appears to be a good baseline standard.
• These figures do not apply to meadows where moisture and soil fertility are considerably higher than normal range lands.